In drilling an oil well, abrasive wear is normally inflicted on the tool joints of the drill string. Efforts have been made in the past to protect tool joints of a drill string. In particular, the tool joints which join sections of the drill collars and drill pipe have been reinforced by various hardfacing, coatings, sleeves or reinforcings. Typically, such materials have utilized tungsten carbide at or around the tool joint. As exemplified in U.S. Pat. No. 3,993,368, one such apparatus has been adapted. As stated thereat, it is intended to provide a tool joint able to tolerate the wear and tear inflicted on the tool joint through the use of hardfacing material.
A tool joint ordinarily represents an external upset in the drill string. The term "external upset" describes the bulge or enlargement in the drill string which occurs at the pin and box connection which comprises the tool joint. Typically, there is a downwardly facing shoulder of some angular construction and radial extent. This shoulder has heretofore been provided with a hardfacing material to reduce the wear at the shoulder and thereby carry the load placed on the tool joint in the particular region where wear most commonly occurs. For instance, it is possible to obtain from the Hughes Tool Company unitized tool joints with the Hughes-X hardfacing applied to it. According to the advertising for this product, a tungsten carbide hardfacing for tool joints is provided which wears well even when run inside casing. When a drill string extends through a cased hole, there is inevitably some risk that the hardfaced tool joint will rub or otherwise abrade against the casing, itself, metal rubbing against metal, which is highly undesirable. Therefore, great efforts have been made to reduce the risk or danger of the hard metal rubbing against the casing and thereby damaging it.
After a tool joint has been used for a significant period of time, the outer surface is inevitably worn away, mostly in uncased holes in abrasive formations, thereby reducing the physical dimensions. As the tool joint is reduced in diameter, it must eventually be replaced or resurfaced for restoration to the original gauge. The manufacturing process by which resizing to a full gauge diameter poses some problems. Consider, as an example, the following problems in resizing a tool joint. In U.S. Pat. No. 3,993,368, there is disclosed a set of rectangular inserts of hardface material in a surrounding sleeve which is divided into two portions. The surrounding sleeve can be removed, either one or both portions, and can thereafter be replaced. To a great extent, if the worn sleeve is discarded, it will be rather wasteful because a significant portion of the worn sleeve still constitutes useful hardface material in the form of inserts in the sleeve. In that event, an alternate approach is the repair step of placing hardface material on the worn sleeve to build the sleeve back up to the gauge diameter of a new sleeve and thereby restore the tool joint to its original dimensions. Through the use of welding procedures, a supportive metal matrix with tungsten carbide particles can be installed to thereby restore the tool joint to gauge size and condition.
In the repair of worn tool joints equipped with hardfacing, problems can arise. As an example, a tool joint is normally equipped with a cylindrical outer face which is typically worn away. As wearing occurs, the body of the tool joint disappears which inevitably results in a distortion of the adjacent shoulder. The shoulder must typically have specified dimensions which match a set of dimensions found on pipe handling elevators used at the drilling rig. This, however, is difficult to achieve in reconstructing a worn tool joint by simply welding additional hardface material onto the tool joint. Grinding in the field or at a welding shop is inappropriate and probably inefficient.
In the instance where attempts are made to repair as by welding, including the process of welding tungsten carbide particles in a matrix around the downwardly facing elevator shoulder, extradordinary quantities of heat are placed on the tool joint, and the heat warps or damages the tool joint where it connects with the body of the pipe. The present invention provides a tool joint construction with hardfacing which avoids the risk of distortion from excessive heat. The present apparatus overcomes limitations known heretofore which relate primarily to the fact that an external sleeve (formed of one or multiple segments) formed into a cylinder and supporting a number of inserts is positioned about the lower end of the tool joint. More wear occurs at the lower end. The hardfacing materials used in the past tend to wear more rapidly at that area, and, in the event of repairs, such repairs have ordinarily involved placing by welding of additional hardfacing material around the lower end of the tool joint. This requires careful welding in the vicinity of the downwardly facing shoulder which must taper at a specified angle to cooperate with elevators used in handling pipe. Moreover, the heat which is applied in the vicinity of the shoulder at the time of redressing creates warpage on the body of the pipe connected to the tool joint.
From the foregoing, it will be understood that certain limitations on previous methods of tool joint repair must be noted. A second limitation results from placing excessive heat at a tool joint. Excessive heat may well reduce metal strength by reducing the temper of the steel. The limitations based on warpage and heating of the drill pipe proper, particularly in the vicinity of the weld between the tool joint and the drill pipe, must be avoided. A further notable limitation is restraint on the buildup of the wear surface of the tool joint in the near vicinity of the lower end of the tool joint while maintaining a suitable profile for engaging pipe supporting elevators. Pipe supporting elevators are constructed in accordance with an industry standard having an 18.0-degree taper seat. The seat cooperates with an 18.0-degree taper at the lower end of the tool joint. In the event of repair as by building up the outside surface of the tool joint, there is risk that the tool joint profile will not be preserved and thereby create a mismatch between tool joint and elevator profile. Another factor of interest is a limitation on the length of the tool joint. So to speak, an external area of reduced diameter is cut to receive the hardfacing inserts. It is cut on the lower exterior portion of the tool joint just below the box, and such a cut reduces the metal in the body for supporting the tensile stress load transferred from pipe to pipe through the tool joint. It will be appreciated that the box end includes a tapered internal thread on a skirt. As metal is removed to leave room for a circular sleeve supporting hardfacing material, it forms a relatively narrow throat with limited structural material and creates a point of stress concentration. Because this stress concentration must be limited, there is a practical limit on the size of the recess which is cut in the box, and the hardface surface area is thereby limited.
The present apparatus is a hardfacing insert attached to a tool joint having a recessed area which avoids excessive stress concentration in the box. Moreover, it supports a set of tungsten carbide inserts which provide a hardfacing feature without creating stress concentrations in the box and which can further be installed and repaired without warping the connection between the tool joint and the pipe.
The present apparatus is, therefore, summarized as a hardfacing attachment in the form of a pair of semicircular sleeves positioned in a recess on a tool joint. The recessed area does not extend to the weld which affixes the tool joint to the pipe and terminates at a distance such that welding at the recess prevents warpage and resultant damage from heating. The recess further terminates short of the box threads. The recess is shaped to receive the insert and thereby support a plurality of tungsten carbide inserts in a semicircular blank. The tungsten carbide inserts supported on a semicircular sleeve are installed by a friction fit or by brazing. The inserts conform to the taper for the tool joint to enable it to be supported by pipe handling elevators. Moreover, surface dressing after partial wear is permitted.